1. Field of the Invention
The present invention is broadly concerned with improved electrical switchgear for use in electrical transmission and distribution systems which makes use of a novel spring-loaded, fast acting, operator independent mechanism for selectively opening and closing the switchgear contacts. More particularly, it is concerned with switchgear operating mechanisms designed for controlled velocity switch contact opening and closing with positive weld break and external indication of the position of the switch contacts (i.e., either opened or closed) so as to eliminate the possibility of a lineman believing that the contacts are opened when in fact they remain in a closed position. In addition, the invention provides a unique, low cost, threaded bearing support for the shiftable switch contacts.
2. Description of the Prior Art
Electrical utilities make use of a large number and variety of switchgear devices in their transmission and distribution systems. Such devices are used for sectionalizing purposes in order to isolate respective zones for component repair or the like and to provide desirable system coordination. System switchgear of this type may be of the padmounted variety and can include vacuum switches under oil or air dielectric switchgear, the latter typically having pivotal switchblades therein carrying movable switch contacts. In any event, switchgear apparatus used in transmission and distribution systems must have an operating mechanism associated therewith for rapid, safe, sure opening and closing of the switch contacts in order to correspondingly break and make electrical circuits through the gear.
Many switch gear operating mechanisms are of the spring-loaded toggle variety, i.e., they make use of a pair of pivotally interconnected toggle links which are spring-loaded and designed, upon movement of an external handle, to go over center and thereby rapidly shift an interconnected spring contact either toward or away from a mating contact. Such toggle mechanisms can present difficulties in that it is possible for such mechanisms to give a false indication of switch contact opening. Specifically, when a lineman manipulates an external operating handle coupled with a toggle-type mechanism, the mechanism can be moved to an over center position while the contacts remain in engagement. When this occurs, the lineman, perceiving that the operating handle has shifted to a position indicative of contact separation, may falsely believe that the contacts have been separated. As can be appreciated, this is a dangerous situation and should be avoided. However, because of the over center operation inherent in toggle mechanisms, this type of false indication of operation is difficult to avoid. As a consequence, many air dielectric switchgear devices have a window permitting the lineman to visually verify the condition of the switch contacts. Nevertheless, the problem of false indication of operation can be a serious one.
Other, non-toggle types of switch operating mechanisms have also been proposed in the past. Certain of these suffer from the problem that they are not operator independent. That is to say, it is important that switchgear operator mechanisms be designed such that, once a lineman initiates operations thereof, the speed of contact opening and closing be both rapid and independent of further actions on the part of the lineman. This prevents undesirable slow opening or closing of the contacts (which can result in pitting or burning of the contacts due to arcing) or "teasing" of the operating mechanism by the lineman.